1//===- FuzzedDataProvider.h - Utility header for fuzz targets ---*- C++ -* ===//
2//
3// Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
4// See https://llvm.org/LICENSE.txt for license information.
5// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
6//
7//===----------------------------------------------------------------------===//
8// A single header library providing an utility class to break up an array of
9// bytes. Whenever run on the same input, provides the same output, as long as
10// its methods are called in the same order, with the same arguments.
11//===----------------------------------------------------------------------===//
12
13#ifndef LLVM_FUZZER_FUZZED_DATA_PROVIDER_H_
14#define LLVM_FUZZER_FUZZED_DATA_PROVIDER_H_
15
16#include <algorithm>
17#include <array>
18#include <climits>
19#include <cstddef>
20#include <cstdint>
21#include <cstring>
22#include <initializer_list>
23#include <limits>
24#include <string>
25#include <type_traits>
26#include <utility>
27#include <vector>
28
29// In addition to the comments below, the API is also briefly documented at
30// https://github.com/google/fuzzing/blob/master/docs/split-inputs.md#fuzzed-data-provider
31class FuzzedDataProvider {
32 public:
33 // |data| is an array of length |size| that the FuzzedDataProvider wraps to
34 // provide more granular access. |data| must outlive the FuzzedDataProvider.
35 FuzzedDataProvider(const uint8_t *data, size_t size)
36 : data_ptr_(data), remaining_bytes_(size) {}
37 ~FuzzedDataProvider() = default;
38
39 // See the implementation below (after the class definition) for more verbose
40 // comments for each of the methods.
41
42 // Methods returning std::vector of bytes. These are the most popular choice
43 // when splitting fuzzing input into pieces, as every piece is put into a
44 // separate buffer (i.e. ASan would catch any under-/overflow) and the memory
45 // will be released automatically.
46 template <typename T> std::vector<T> ConsumeBytes(size_t num_bytes);
47 template <typename T>
48 std::vector<T> ConsumeBytesWithTerminator(size_t num_bytes, T terminator = 0);
49 template <typename T> std::vector<T> ConsumeRemainingBytes();
50
51 // Methods returning strings. Use only when you need a std::string or a null
52 // terminated C-string. Otherwise, prefer the methods returning std::vector.
53 std::string ConsumeBytesAsString(size_t num_bytes);
54 std::string ConsumeRandomLengthString(size_t max_length);
55 std::string ConsumeRandomLengthString();
56 std::string ConsumeRemainingBytesAsString();
57
58 // Methods returning integer values.
59 template <typename T> T ConsumeIntegral();
60 template <typename T> T ConsumeIntegralInRange(T min, T max);
61
62 // Methods returning floating point values.
63 template <typename T> T ConsumeFloatingPoint();
64 template <typename T> T ConsumeFloatingPointInRange(T min, T max);
65
66 // 0 <= return value <= 1.
67 template <typename T> T ConsumeProbability();
68
69 bool ConsumeBool();
70
71 // Returns a value chosen from the given enum.
72 template <typename T> T ConsumeEnum();
73
74 // Returns a value from the given array.
75 template <typename T, size_t size> T PickValueInArray(const T (&array)[size]);
76 template <typename T, size_t size>
77 T PickValueInArray(const std::array<T, size> &array);
78 template <typename T> T PickValueInArray(std::initializer_list<const T> list);
79
80 // Writes data to the given destination and returns number of bytes written.
81 size_t ConsumeData(void *destination, size_t num_bytes);
82
83 // Reports the remaining bytes available for fuzzed input.
84 size_t remaining_bytes() { return remaining_bytes_; }
85
86 private:
87 FuzzedDataProvider(const FuzzedDataProvider &) = delete;
88 FuzzedDataProvider &operator=(const FuzzedDataProvider &) = delete;
89
90 void CopyAndAdvance(void *destination, size_t num_bytes);
91
92 void Advance(size_t num_bytes);
93
94 template <typename T>
95 std::vector<T> ConsumeBytes(size_t size, size_t num_bytes);
96
97 template <typename TS, typename TU> TS ConvertUnsignedToSigned(TU value);
98
99 const uint8_t *data_ptr_;
100 size_t remaining_bytes_;
101};
102
103// Returns a std::vector containing |num_bytes| of input data. If fewer than
104// |num_bytes| of data remain, returns a shorter std::vector containing all
105// of the data that's left. Can be used with any byte sized type, such as
106// char, unsigned char, uint8_t, etc.
107template <typename T>
108std::vector<T> FuzzedDataProvider::ConsumeBytes(size_t num_bytes) {
109 num_bytes = std::min(a: num_bytes, b: remaining_bytes_);
110 return ConsumeBytes<T>(num_bytes, num_bytes);
111}
112
113// Similar to |ConsumeBytes|, but also appends the terminator value at the end
114// of the resulting vector. Useful, when a mutable null-terminated C-string is
115// needed, for example. But that is a rare case. Better avoid it, if possible,
116// and prefer using |ConsumeBytes| or |ConsumeBytesAsString| methods.
117template <typename T>
118std::vector<T> FuzzedDataProvider::ConsumeBytesWithTerminator(size_t num_bytes,
119 T terminator) {
120 num_bytes = std::min(a: num_bytes, b: remaining_bytes_);
121 std::vector<T> result = ConsumeBytes<T>(num_bytes + 1, num_bytes);
122 result.back() = terminator;
123 return result;
124}
125
126// Returns a std::vector containing all remaining bytes of the input data.
127template <typename T>
128std::vector<T> FuzzedDataProvider::ConsumeRemainingBytes() {
129 return ConsumeBytes<T>(remaining_bytes_);
130}
131
132// Returns a std::string containing |num_bytes| of input data. Using this and
133// |.c_str()| on the resulting string is the best way to get an immutable
134// null-terminated C string. If fewer than |num_bytes| of data remain, returns
135// a shorter std::string containing all of the data that's left.
136inline std::string FuzzedDataProvider::ConsumeBytesAsString(size_t num_bytes) {
137 static_assert(sizeof(std::string::value_type) == sizeof(uint8_t),
138 "ConsumeBytesAsString cannot convert the data to a string.");
139
140 num_bytes = std::min(a: num_bytes, b: remaining_bytes_);
141 std::string result(
142 reinterpret_cast<const std::string::value_type *>(data_ptr_), num_bytes);
143 Advance(num_bytes);
144 return result;
145}
146
147// Returns a std::string of length from 0 to |max_length|. When it runs out of
148// input data, returns what remains of the input. Designed to be more stable
149// with respect to a fuzzer inserting characters than just picking a random
150// length and then consuming that many bytes with |ConsumeBytes|.
151inline std::string
152FuzzedDataProvider::ConsumeRandomLengthString(size_t max_length) {
153 // Reads bytes from the start of |data_ptr_|. Maps "\\" to "\", and maps "\"
154 // followed by anything else to the end of the string. As a result of this
155 // logic, a fuzzer can insert characters into the string, and the string
156 // will be lengthened to include those new characters, resulting in a more
157 // stable fuzzer than picking the length of a string independently from
158 // picking its contents.
159 std::string result;
160
161 // Reserve the anticipated capacity to prevent several reallocations.
162 result.reserve(res: std::min(a: max_length, b: remaining_bytes_));
163 for (size_t i = 0; i < max_length && remaining_bytes_ != 0; ++i) {
164 char next = ConvertUnsignedToSigned<char>(value: data_ptr_[0]);
165 Advance(num_bytes: 1);
166 if (next == '\\' && remaining_bytes_ != 0) {
167 next = ConvertUnsignedToSigned<char>(value: data_ptr_[0]);
168 Advance(num_bytes: 1);
169 if (next != '\\')
170 break;
171 }
172 result += next;
173 }
174
175 result.shrink_to_fit();
176 return result;
177}
178
179// Returns a std::string of length from 0 to |remaining_bytes_|.
180inline std::string FuzzedDataProvider::ConsumeRandomLengthString() {
181 return ConsumeRandomLengthString(max_length: remaining_bytes_);
182}
183
184// Returns a std::string containing all remaining bytes of the input data.
185// Prefer using |ConsumeRemainingBytes| unless you actually need a std::string
186// object.
187inline std::string FuzzedDataProvider::ConsumeRemainingBytesAsString() {
188 return ConsumeBytesAsString(num_bytes: remaining_bytes_);
189}
190
191// Returns a number in the range [Type's min, Type's max]. The value might
192// not be uniformly distributed in the given range. If there's no input data
193// left, always returns |min|.
194template <typename T> T FuzzedDataProvider::ConsumeIntegral() {
195 return ConsumeIntegralInRange(std::numeric_limits<T>::min(),
196 std::numeric_limits<T>::max());
197}
198
199// Returns a number in the range [min, max] by consuming bytes from the
200// input data. The value might not be uniformly distributed in the given
201// range. If there's no input data left, always returns |min|. |min| must
202// be less than or equal to |max|.
203template <typename T>
204T FuzzedDataProvider::ConsumeIntegralInRange(T min, T max) {
205 static_assert(std::is_integral<T>::value, "An integral type is required.");
206 static_assert(sizeof(T) <= sizeof(uint64_t), "Unsupported integral type.");
207
208 if (min > max)
209 abort();
210
211 // Use the biggest type possible to hold the range and the result.
212 uint64_t range = static_cast<uint64_t>(max) - static_cast<uint64_t>(min);
213 uint64_t result = 0;
214 size_t offset = 0;
215
216 while (offset < sizeof(T) * CHAR_BIT && (range >> offset) > 0 &&
217 remaining_bytes_ != 0) {
218 // Pull bytes off the end of the seed data. Experimentally, this seems to
219 // allow the fuzzer to more easily explore the input space. This makes
220 // sense, since it works by modifying inputs that caused new code to run,
221 // and this data is often used to encode length of data read by
222 // |ConsumeBytes|. Separating out read lengths makes it easier modify the
223 // contents of the data that is actually read.
224 --remaining_bytes_;
225 result = (result << CHAR_BIT) | data_ptr_[remaining_bytes_];
226 offset += CHAR_BIT;
227 }
228
229 // Avoid division by 0, in case |range + 1| results in overflow.
230 if (range != std::numeric_limits<decltype(range)>::max())
231 result = result % (range + 1);
232
233 return static_cast<T>(static_cast<uint64_t>(min) + result);
234}
235
236// Returns a floating point value in the range [Type's lowest, Type's max] by
237// consuming bytes from the input data. If there's no input data left, always
238// returns approximately 0.
239template <typename T> T FuzzedDataProvider::ConsumeFloatingPoint() {
240 return ConsumeFloatingPointInRange<T>(std::numeric_limits<T>::lowest(),
241 std::numeric_limits<T>::max());
242}
243
244// Returns a floating point value in the given range by consuming bytes from
245// the input data. If there's no input data left, returns |min|. Note that
246// |min| must be less than or equal to |max|.
247template <typename T>
248T FuzzedDataProvider::ConsumeFloatingPointInRange(T min, T max) {
249 if (min > max)
250 abort();
251
252 T range = .0;
253 T result = min;
254 constexpr T zero(.0);
255 if (max > zero && min < zero && max > min + std::numeric_limits<T>::max()) {
256 // The diff |max - min| would overflow the given floating point type. Use
257 // the half of the diff as the range and consume a bool to decide whether
258 // the result is in the first of the second part of the diff.
259 range = (max / 2.0) - (min / 2.0);
260 if (ConsumeBool()) {
261 result += range;
262 }
263 } else {
264 range = max - min;
265 }
266
267 return result + range * ConsumeProbability<T>();
268}
269
270// Returns a floating point number in the range [0.0, 1.0]. If there's no
271// input data left, always returns 0.
272template <typename T> T FuzzedDataProvider::ConsumeProbability() {
273 static_assert(std::is_floating_point<T>::value,
274 "A floating point type is required.");
275
276 // Use different integral types for different floating point types in order
277 // to provide better density of the resulting values.
278 using IntegralType =
279 typename std::conditional<(sizeof(T) <= sizeof(uint32_t)), uint32_t,
280 uint64_t>::type;
281
282 T result = static_cast<T>(ConsumeIntegral<IntegralType>());
283 result /= static_cast<T>(std::numeric_limits<IntegralType>::max());
284 return result;
285}
286
287// Reads one byte and returns a bool, or false when no data remains.
288inline bool FuzzedDataProvider::ConsumeBool() {
289 return 1 & ConsumeIntegral<uint8_t>();
290}
291
292// Returns an enum value. The enum must start at 0 and be contiguous. It must
293// also contain |kMaxValue| aliased to its largest (inclusive) value. Such as:
294// enum class Foo { SomeValue, OtherValue, kMaxValue = OtherValue };
295template <typename T> T FuzzedDataProvider::ConsumeEnum() {
296 static_assert(std::is_enum<T>::value, "|T| must be an enum type.");
297 return static_cast<T>(
298 ConsumeIntegralInRange<uint32_t>(min: 0, max: static_cast<uint32_t>(T::kMaxValue)));
299}
300
301// Returns a copy of the value selected from the given fixed-size |array|.
302template <typename T, size_t size>
303T FuzzedDataProvider::PickValueInArray(const T (&array)[size]) {
304 static_assert(size > 0, "The array must be non empty.");
305 return array[ConsumeIntegralInRange<size_t>(min: 0, max: size - 1)];
306}
307
308template <typename T, size_t size>
309T FuzzedDataProvider::PickValueInArray(const std::array<T, size> &array) {
310 static_assert(size > 0, "The array must be non empty.");
311 return array[ConsumeIntegralInRange<size_t>(min: 0, max: size - 1)];
312}
313
314template <typename T>
315T FuzzedDataProvider::PickValueInArray(std::initializer_list<const T> list) {
316 // TODO(Dor1s): switch to static_assert once C++14 is allowed.
317 if (!list.size())
318 abort();
319
320 return *(list.begin() + ConsumeIntegralInRange<size_t>(0, list.size() - 1));
321}
322
323// Writes |num_bytes| of input data to the given destination pointer. If there
324// is not enough data left, writes all remaining bytes. Return value is the
325// number of bytes written.
326// In general, it's better to avoid using this function, but it may be useful
327// in cases when it's necessary to fill a certain buffer or object with
328// fuzzing data.
329inline size_t FuzzedDataProvider::ConsumeData(void *destination,
330 size_t num_bytes) {
331 num_bytes = std::min(a: num_bytes, b: remaining_bytes_);
332 CopyAndAdvance(destination, num_bytes);
333 return num_bytes;
334}
335
336// Private methods.
337inline void FuzzedDataProvider::CopyAndAdvance(void *destination,
338 size_t num_bytes) {
339 std::memcpy(dest: destination, src: data_ptr_, n: num_bytes);
340 Advance(num_bytes);
341}
342
343inline void FuzzedDataProvider::Advance(size_t num_bytes) {
344 if (num_bytes > remaining_bytes_)
345 abort();
346
347 data_ptr_ += num_bytes;
348 remaining_bytes_ -= num_bytes;
349}
350
351template <typename T>
352std::vector<T> FuzzedDataProvider::ConsumeBytes(size_t size, size_t num_bytes) {
353 static_assert(sizeof(T) == sizeof(uint8_t), "Incompatible data type.");
354
355 // The point of using the size-based constructor below is to increase the
356 // odds of having a vector object with capacity being equal to the length.
357 // That part is always implementation specific, but at least both libc++ and
358 // libstdc++ allocate the requested number of bytes in that constructor,
359 // which seems to be a natural choice for other implementations as well.
360 // To increase the odds even more, we also call |shrink_to_fit| below.
361 std::vector<T> result(size);
362 if (size == 0) {
363 if (num_bytes != 0)
364 abort();
365 return result;
366 }
367
368 CopyAndAdvance(destination: result.data(), num_bytes);
369
370 // Even though |shrink_to_fit| is also implementation specific, we expect it
371 // to provide an additional assurance in case vector's constructor allocated
372 // a buffer which is larger than the actual amount of data we put inside it.
373 result.shrink_to_fit();
374 return result;
375}
376
377template <typename TS, typename TU>
378TS FuzzedDataProvider::ConvertUnsignedToSigned(TU value) {
379 static_assert(sizeof(TS) == sizeof(TU), "Incompatible data types.");
380 static_assert(!std::numeric_limits<TU>::is_signed,
381 "Source type must be unsigned.");
382
383 // TODO(Dor1s): change to `if constexpr` once C++17 becomes mainstream.
384 if (std::numeric_limits<TS>::is_modulo)
385 return static_cast<TS>(value);
386
387 // Avoid using implementation-defined unsigned to signed conversions.
388 // To learn more, see https://stackoverflow.com/questions/13150449.
389 if (value <= std::numeric_limits<TS>::max()) {
390 return static_cast<TS>(value);
391 } else {
392 constexpr auto TS_min = std::numeric_limits<TS>::min();
393 return TS_min + static_cast<TS>(value - TS_min);
394 }
395}
396
397#endif // LLVM_FUZZER_FUZZED_DATA_PROVIDER_H_
398

source code of compiler-rt/include/fuzzer/FuzzedDataProvider.h